>IR. SOLLY ON THE POTATO MUIUIAIN. 41 



Azotised matter in tliat condition necessary to its acting as a 

 ferment, may exist in plants from two causes ; the partial decom- 

 position of gluten and albumen already formed, or t'ne imperfect 

 and incomplete formation of these substances : either of these 

 causers miglit account for the effects under consideration, and it 

 is by no means a simple problem to determine to which of these 

 two it is really due. The fact that no epidemic of this kind has 

 been observed for many years, shows that the cause must be 

 complicated, depending upon a combination of several condi- 

 tions, which do not frequently occur together. In the present 

 season, and at a time when the plants were in full growth and 

 vigour, there happened several very remarkable alterations of 

 weather, and from hot and dry there was a rapid transition to 

 cold and damp ; evaporation being checked in a sudden and un- 

 usual manner. At the same time that evaporation was thus 

 diminished whilst growth continued, the influence of light was 

 also to a great extent impeded ; a continuance of cloudy weather 

 ensuing, the effect of which was very materially to reduce t!ie 

 whole quantity of sunshine during that period. Amongst the 

 causes wliich may possibly have contributed to cause an un- 

 healthy state of growth in plants, light certainly is not the least 

 important ; and it must be remembered that besides being defi- 

 cient in absolute quality, it may also have been deficient in che- 

 mical power. It is much to be regretted that we have as yet 

 no record of the diurnal amount of chemical rays which reach 

 the earth, and consequently have no means of judging of the 

 amount of influence which may be due to this cause, I have 

 endeavoured, though in vain, to ascertain whether any peculiar 

 deficiency in chemical power has been observed by those who 

 were experimenting with light during the past summer. 



The potato rot manifested itself in two distinct forms this 

 year, — the one a true putrid fermentation or wet rot, in which the 

 whole tuber soon became converted into a brown shiny foetid 

 mass ; the other a less rapid decay, in which the tuber slowly 

 became converted into a brown spongy matter. The presence 

 of water and putrefying azotised matter, and a moderate or ele- 

 vated temperature, were requisite for the former; whilst the lat- 

 ter, which more resembled erem.acausis, prevailed, when less water 

 and little or no putrid azotised matter existed in the tubers. Botli 

 forms of disease are however arrested by cold and dryness, decay 

 ceasing to spread, and the diseased pai'ts shrivelling up, a kind 

 of false skin in some cases forming between the sound and the 

 decayed part, which effectually prevents further decay. 



A few isolated cases of diseased tubers, formed in houses, 

 under peculiar circumstances, from tubers of last year, have 

 been observed. Two cases of this kind have been mentioned to 



